[PATCH] CFI: fix panic in kernel bpf map traversal

[Eric Yan]

During BPF map iterator test, 'bpf_for_each_map_elem' call failed on
Android common kernel kernel5.15/6.1 with clang CFI enabled.
It has been found that the "callback_fn" parameter received by
bpf_for_each_map_elem is the address of the jitted BPF program code,
which is not in the kernel text section, leads to kernel panic in
__cfi_slowpath_diag check. so, just disable CFI for bpf map iterator.

same crash message on a typical arm64 debian kernel is as follows:
Kernel panic - not syncing: CFI failure (target: bpf_prog_xx+0x0/0x560)
CPU: 0 PID: 0 Comm: swapper/0 Kdump: loaded Not tainted 5.15.0+ #1
Hardware name: linux,dummy-virt (DT)
Call trace:
 dump_backtrace.cfi_jt+0x0/0x4
 show_stack+0x30/0x3c
 __dump_stack+0x28/0x34
 dump_stack_lvl+0x74/0xc0
 dump_stack+0x14/0x1c
 panic+0x2b8/0x588
 __cfi_slowpath_diag+0x0/0x78
 __cfi_slowpath_diag+0x6c/0x78
 bpf_for_each_hash_elem+0x228/0x304
 bpf_for_each_map_elem+0xac/0xc0
 bpf_prog_8aad3428fbe59598_F+0x184/0x6c4
 bpf_dispatcher_nop_func.17066+0xc/0x14
 bpf_trace_run1+0x1d4/0x208
 __bpf_trace_sched_wakeup_template+0x4c/0x74
 __traceiter_sched_wakeup+0x13c/0x170
 trace_sched_wakeup+0xf4/0x108
 ttwu_do_wakeup+0x58/0x17c

sample bpf testing code:
(based on ahttps://github.com/iovisor/bcc/blob/master/libbpf-tools/wakeuptime.bpf.c#L54)

static long chk_item(struct bpf_map *map, const void *key, void *value, void *cttx) {
        bpf_printk("key: %llx\n", key);
        return 0;
}
static int wakeup(void *ctx, struct task_struct *p) {
        ...
        if (delta > 1000000)
                bpf_for_each_map_elem(&counts, chk_item, NULL, 0);
}

Signed-off-by: Eric Yan <eric.yan@xxxxxxxx>
---
 kernel/bpf/arraymap.c | 2 +-
 kernel/bpf/hashtab.c  | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/bpf/arraymap.c b/kernel/bpf/arraymap.c
index 2058e89b5ddd..4cd400082236 100644
--- a/kernel/bpf/arraymap.c
+++ b/kernel/bpf/arraymap.c
@@ -686,7 +686,7 @@ static const struct bpf_iter_seq_info iter_seq_info = {
        .seq_priv_size          = sizeof(struct bpf_iter_seq_array_map_info),
 };

-static long bpf_for_each_array_elem(struct bpf_map *map, bpf_callback_t callback_fn,
+static long __nocfi bpf_for_each_array_elem(struct bpf_map *map, bpf_callback_t callback_fn,
                                    void *callback_ctx, u64 flags)
 {
        u32 i, key, num_elems = 0;
diff --git a/kernel/bpf/hashtab.c b/kernel/bpf/hashtab.c
index 56d3da7d0bc6..59e337f446d0 100644
--- a/kernel/bpf/hashtab.c
+++ b/kernel/bpf/hashtab.c
@@ -2132,7 +2132,7 @@ static const struct bpf_iter_seq_info iter_seq_info = {
        .seq_priv_size          = sizeof(struct bpf_iter_seq_hash_map_info),
 };

-static long bpf_for_each_hash_elem(struct bpf_map *map, bpf_callback_t callback_fn,
+static long __nocfi bpf_for_each_hash_elem(struct bpf_map *map, bpf_callback_t callback_fn,
                                   void *callback_ctx, u64 flags)
 {
        struct bpf_htab *htab = container_of(map, struct bpf_htab, map);
--
2.25.1

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